Study on the Emission Properties of the Impregnated Cathode With Nanoparticle Films

Abstract

The effect of thin-film characteristics on the thermionic emission of dispenser cathodes has been investigated. Nanoparticle Ir thin films were grown by magnetron sputtering at room temperature. Microstructures of these thin films grown at different sputtering pressures were observed using a scanning electron microscope. The results showed that the particle size of the films depended on the deposition rate in the nucleation stage of the Ir films, which could be well controlled by the sputtering pressure. N-type cathodes were fabricated by impregnating tungsten matrices of 25% porosity with 6:1:2-type barium calcium aluminate and then coating them with nanoparticle Ir thin films, 200-500 nm in thickness, in hydrogen at 1200 • C. A comparison was made in the emission uniformity between an N-type cathode (defined here as a Ba dispenser cathode coated with a layer of metal nanoparticles) and a traditional M-type cathode using a thermionic electron microscope. The chemical components of the vacuum background, the evaporants from an N-type cathode, and an M-type cathode were respectively analyzed using a time-of-flight mass spectrometer. The evaporating rates of the two types of cathodes and their dependence on the cathode temperatures were also investigated. Finally, the electron emission performance of the N-type cathodes was studied.

纳米粒子薄膜热电子发射性能

“…场发射阴极的发射电流密度较大, 但由于它的总电流 偏小, 且发射不均匀, 稳定性差, 以及制备复杂等因素, 从而大大限制了它的应用. 为此, 在基于覆膜 阴极研究工作的基础上, 我们提出了一种新型阴极的思路, 即在钡钨基体表面沉积一层厚度为 100∼ 1000 nm 的金属纳米粒子薄膜, 以此来降低钡钨基底表面的逸出功, 进而提高电子发射体的发射电流 密度 [19,20] . 纳米结构薄膜是由颗粒尺寸为小于 100 nm 的粒子为主体形成的薄膜.…”

“…纳米材料的发射特 性研究, 已成为国际研究领域的一个热点 [21,22] . 我们对纳米粒子所组成薄膜的热辐射特性和发射均 匀性进行了初步的研究 [23,24] , 发现这种材料具有非常强的热辐射特性和很好的发射均匀性. 本论文 将利用热电子发射的基本理论并结合最新覆膜电子发射体发射理论, 研究这种新型电子发射体的发射 机理, 对电子发射的理论和应用以及拓展纳米材料应用研究领域都具有十分重要的学术和应用价值.…”

“…根据相同时间内到达探测器的离子数就可计算出该种成分在样品中的含量. [25] ν = aI, 米粒子薄膜阴极在高的直流发射电流密度的情况下与低温低电流密度一样 [20] , 也具有良好的发射均 匀性. 目前直流发射电流密度达到 30 A/cm 2 实用热阴极未见报道.…”

Correlation between microstructure and thermionic electron emission from Os-Ru thin films on dispenser cathodes

“…However, no information on crystal structure or grain orientation was presented. 13 Green et al and Brion et al studied Os-W coatings and the phases that developed in the coating during cathode operation. 7,8 They found that the formation of a r-phase alloy correlated with enhanced emission.…”

A new type of photocathode driven by a laser

“…这种材料的发射特性研究, 已成为国际研究领域的 一个热点 [32,33] . 我们对纳米粒子所组成薄膜的热辐射特性 [34] 、热发射均匀性 [35,36] 进行了研究, 发现 这种材料具有非常强的热辐射特性和很好的发射均匀性. 本文将利用光电发射的基本理论, 研究这种 新型电子发射体的发射性能, 这对拓展纳米材料应用研究领域具有十分重要的学术价值和应用价值.…”